Science of Games: Zombies, part 1

The first edition of our new bi-monthly column digs into the science behind mankind’s most feared “imaginary” enemy

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We thought we’d launch our new column with a somewhat timely topic. Naughty Dog recently announced their new project, The Last of Us, which prominently features a humanoid creature that appears, at first blush, to be quite zombie-like. One of the most intriguing parts of Naughty Dog’s announcement of The Last of Us is that it has posted videos of so-called “zombie ants” from the Thailand rainforest on the game’s official website. These videos could simply be creepy ambience to prime gamers for a discussion about the zombie apocalypse, or they could hint at a plot point in the upcoming game. We’ll playfully assume the latter.

The Zombie AntsSince being introduced to the world via BBC documentaries, the carpenter ants under the effects of a type of fungus called Cordyceps have become superstars of the geek world, and are now the flavor-of-the-month theory for many zombie predictions. Basically, once infected, these ants start to exhibit zombie-like behavior. This isn’t some crackpot theory. This is well-documented biology.

The most incredible part about this as a zombie-theory is that theoretical zombie parasites act in much the same way. The infection is on a mission to spread itself as far as possible. In this case, it does that by marching the host body onto the underside of a leaf around high noon in preparation to explode spores onto the jungle floor below (as opposed to a classic zombie, which marches its body into populated areas). Researchers note that it does this around noon (yes, it really does pick a specific time) so that the fungus will have plenty of time to grow out of the ant’s head during the cooler nighttime.

Where many go wrong is in assuming this fungus could mutate in order to affect humans in a similar way. Suffice to say that the human nervous system is quite a bit more complex than that of an ant. Moreover, evolution of these sorts of abilities takes tens of millions of years. Thinking that one day this fungus will suddenly have the staggering complexity to control a human nervous system in a very specific way is just as absurd as thinking one day a fish was born with legs and waltzed onto dry land.

That said, there are already parasites that have been honing this ability for millions of years in humans, and are surprisingly adept at it.

Toxoplasma GondiiIn no way does Toxoplasma Gondii create human zombies that are in any way similar to the infamous zombie ants. However, you may be surprised at how widespread and influential these brain parasites actually are.

Researchers have said that this parasite is present in 20-60 percent of the population of most countries, depending on factors like hygiene standards and cooking practices (it’s most commonly spread through poorly cooked meat and contact with feces). The parasite tends to come from the intestines of cats, and is usually fairly harmless in human beings. However, research has shown that people infected with Toxoplasma Gondii are diagnosed with schizophrenia at a higher rate, generally have slower reaction times, and are six times more likely to be involved in traffic accidents.

But that’s not all. While benign in most adults (remember that it’s already in at least 20 percent of us, so if it was really bad, you’d know about it) it can actually be fatal to infants and fetuses. Which, fun fact, is the reason why pregnant women are supposed to stay away from cat litter. Because, as previously mentioned, the parasite is common in the digestive systems of cats.

If the parasite develops into a full-blown disease, the infected person first experiences flu-like symptoms, and afterward may (in uncommon cases) develop symptoms like depression. If that doesn’t sound like the beginning of a zombie movie, we’re not sure what does. So if a friend or loved one has the flu, be careful: they could be Patient Zero.

IschemiaAt this year’s San Diego Comic-Con, the publisher of Dead Island put together an awesome panel called “The Science of Zombies: How Possible is a Zombie Virus?” (I had the incredible pleasure of speaking on it. /brag.) On the panel were distinguished scholars, including a Harvard professor of medicine and two neuroscientists. One of these people, Dr. Bradley Voytek, has studied the zombie brain in detail. He’s even gone so far as to work with colleagues to create a mock-MRI of what the zombie brain would look like in real life.

We talked with him for this article, and discussed his research along with a number of credible zombie theories. Voytek’s mock-up of the zombie brain shows a mind with massively reduced activity along with some over-activity in the sectors of the brain that control aggression. However, what we were curious about is whether this mangled zombie brain could actually still support its own body. “In very extreme cases, huge swathes of the brain have been damaged and--although the person may have certain cognitive or behavioral deficits--they're very much alive,” said Voytek.

What’s interesting is the way in which that brain damage might be caused. Almost all varieties of zombie feature a moment of death and a resurrection. But even if a virus was able to retake control over the body that it kills, the body would still undergo damage during the time it was dead. A lack of oxygen and nutrients flowing to the brain and other organs causes what is called ischemic damage.

The brain quickly accumulates damage that is often irreversible. “Certain brain regions, such as the hippocampus (which is required for memory formation) can be damaged with only a few minutes without oxygen,” said Voytek. “The hippocampus, and other parts of the limbic system of which it's a part, make up a big part of what we think is damaged in the zombie brain.”

The best part about this theory is that it can account for different types of zombies. A virus or parasite that resurrects its host quickly could create more intelligent zombies as it would only have hosts with some brain damage. If the host stayed dead for longer, they’d be dumber but also less sensitive to pain.